1. Field of the Invention
The present invention relates to a device for recording, reproducing, or erasing information on a disk-shaped optical information recording medium (hereinafter referred to as an "optical information recording/reproducing device") and a method for the same. In particular, the present invention relates to a device and a method for recording, reproducing, or erasing information on an optical disk which utilizes both groove regions (defining "groove tracks") and land regions between grooves (defining "land tracks") as information tracks, the groove regions and the land regions having been previously formed on a disk substrate.
2. Description of the Related Art
In recent years, a great deal of research and development effort has been made in order to realize optical information recording media for recording and reproducing information data (e.g., video data and audio data) thereon. One example of such an optical information recording medium is an optical disk. A rewritable optical disk includes guide grooves (hereinafter referred to as "grooves") previously engraved on an optical disk substrate, the grooves being utilized as information tracks. Any region existing between adjoining grooves is referred to as a "land". Information can be recorded on or reproduced from the optical disk by converging a laser beam on the flat portions of grooves or lands. The information or data which users can record on an information recording medium at their own discretion will be referred to as "user data", as opposed to data that is previously recorded on the information recording medium.
In the case of commercially-available optical disks, information is typically recorded in either the groove region or the land region, the other region serving as a guard band for separating adjoining grooves or lands. When information signals are recorded in the grooves, for example, the lands serve as guard bands for separating adjoining information tracks defined by the grooves. Rewritable optical disks typically carries identification data which is previously recorded on the disk in the form of concave/convex pits (which are commonly referred to as "pre-pits"). Such pre-pits indicate location information (e.g., sector addresses) on the disk.
A technique for increasing the recording density of an optical disk is disclosed in Japanese Patent Publication No. 63-57859, where the track density is increased essentially by utilizing both grooves and lands as information tracks, i.e., by recording information on both grooves and lands (which are hence referred to as "groove tracks" and "land tracks", respectively). On the other hand, rewritable optical disks require the above-mentioned identification data, which represent location information and the like, to be previously recorded on the disk for enabling access by a user. Accordingly, the inventors of the present invention have proposed in Japanese Laid-Open Patent Publication No. 6-176404 (corresponding to U.S. Pat. No. 5,452,284) a technique of recording one identification data for an adjoining pair consisting of a groove and a land, the identification signal being recorded in a position between the groove and the land, whereby the manufacturing process of an optical disk is simplified. Hereinafter, such identification data, recorded in a position between an adjoining pair consisting of a groove track and a land track, will be referred to as an "intermediate address"; and the method of recording identification data in the form of an intermediate address shared by adjoining information tracks will be referred to as an "intermediate address method".
By referring to the figures, the concept of intermediate address will be described below, with respect to a tracking control method for reading information on an optical disk, and a method of reading an intermediate address signal.
FIGS. 12A and 12B schematically show the structure of a conventional optical disk 200 having sectors 202. As shown in FIG. 12A, the conventional optical disk 200 includes an information track(s) 201 formed in a spiral or concentric shape on a disk substrate. As shown in FIG. 12B, the information tracks 201 are divided into sectors 202, each sector 202 including a header region 203 (in which identification data is recorded) and a data region 204.
FIG. 13 shows the structure of information tracks of the conventional optical disk 200, where the above-described intermediate address method is adopted. As shown in FIG. 13, the information tracks 201 include groove tracks 208 and land tracks 209 alternately formed adjacent to each other. Within the data region 204, data is recorded in the form of recording marks 207 on both the groove track 208 and the land track 209. Within the header region 203, identification data is recorded in the form of pre-pits (address pits) 206. The data recorded on the information tracks 201 can be reproduced by the use of a beam spot 201.
As shown in FIG. 13, the groove track 208 and the land track 209 have the same width and the same track pitch of Tp. The address pits 206 are formed in such a manner that the center lines thereof are shifted from the center line of the corresponding groove track 208 by Tp/2 along the radius direction of the disk substrate (i.e., perpendicularly to the direction along which the information tracks 201 extends). The address pits 206 are provided on the boundaries between the groove track 208 and the land track 209 at a pitch of 2 Tp (i.e., so as to be provided on every other boundary between the groove track 208 and the land track 209).
FIG. 14 is a schematic block diagram illustrating an optical information recording/reproducing device 400 for recording or reproducing information on a conventional optical disk 200. It is assumed that the conventional optical disk 200 has an information track 201 (i.e., a groove track 208 or a land track 209) thereon as shown in the structure of FIG. 13. The optical information recording/reproducing device 400 (FIG. 14) includes an optical disk drive and a host computer 239. The optical disk drive includes an optical head 410, a tracking control/drive section 420, a reproduced signal processing section 430, a recording signal processing section 440, a spindle motor 236 for rotating the optical disk 200, and a system controller 237.
The optical head 410 includes a semiconductor laser 211, a collimation lens 212 for collimating laser light emitted from the semiconductor laser 211, a half mirror 213 located in the path of the collimated light, an objective lens 214 for converging the collimated light led through the half mirror 213 onto an information surface of the optical disk 200, and an actuator 216 supporting the objective lens 214. Thus, a beam spot is radiated on the information track 201 of the optical disk 200. The optical head 410 further includes an optical detector 215 for receiving light reflected from the optical disk 200 via the objective lens 214 and the half mirror 213. The optical detector 215 includes two light receiving portions 215a and 215b for generating a tracking error signal, the light receiving portions 215a and 215b defining two integral portions of the optical detector 215 divided in parallel to the direction along which the information track 201 extends. The semiconductor laser 211, the collimation lens 212, the half mirror 213, the object lens 214, the optical detector 215, and the actuator 216 are mounted on a head base (not shown), thus composing the optical head 410.
The tracking control/drive section 420 includes: a differential amplifier 218 for receiving the detected signals from the light receiving portions 215a and 215b of the optical detector 215 and outputting a signal representing a difference therebetween; a low-pass filter (LPF) 219 for receiving the differential signal; a polarity inversion circuit 220; a tracking control circuit 221; and a driving circuit 222. The LPF 219 subjects the differential signal from the differential amplifier 218 to a predetermined filtering process, and outputs a signal S1 to the polarity inversion circuit 220. The polarity inversion circuit 220 receives the signal S1 from the LPF 219 and a control signal L1 from the system controller 237 (described later), and outputs a signal S2 to the tracking control circuit 221. The tracking control circuit 221 receives the signal S2 from the polarity inversion circuit 220 and outputs a tracking control signal to the driving circuit 222. The driving circuit 222 receives the tracking control signal from the tracking control circuit 221 and outputs a driving current to the actuator 216.
The reproduced signal processing section 430 includes: an additive amplifier 223 for outputting a signal (addition signal) representing a sum of the detected signals from the light receiving portions 215a and 215b of the optical detector 215; a waveform equalization circuit 224 for receiving the addition signal and converting the frequency characteristics thereof; a data slice circuit 225 for receiving the output of the waveform equalization circuit 224 and outputting a digitized signal; a PLL (phase locked loop) 226 for generating a reproduction clock signal which is in synchronization with the digitized signal and outputting a digital reproduced signal in synchronization with the reproduction clock signal; an AM (address mark) detection circuit 227 and a selector 228 for receiving the digital reproduced signal; a data demodulation circuit 229; an error correction circuit 230; an address demodulation circuit 231; and an error detection circuit 232.
The AM detection circuit 227 receives a digital reproduced signal from the PLL 226 and outputs a control signal L2 to the selector 228. The selector 228 receives the digital reproduced signal from the PLL 226 and the control signal L2 from the AM detection circuit 227, and outputs the digital reproduced signal to a selected one of the data demodulation circuit 229 and the address demodulation circuit 231. The data demodulation circuit 229 receives the digital reproduced signal via the selector 228 and outputs demodulated data to the error correction circuit 230. The error correction circuit 230 receives the demodulated data from the data demodulation circuit 229 and outputs decoded data to the host computer 239. The address demodulation circuit 231 receives the digital reproduced signal via the selector 228 and outputs a demodulated address to the error detection circuit 232. The error detection circuit 232 receives the demodulated address from the address demodulation circuit 231 and outputs address data to the system controller 237.
The recording signal processing section 440 includes a recording signal processing circuit 234 and a laser driving circuit 235. The recording signal processing circuit 234 receives information signals representing e.g., digital video/audio data from the host computer 239 and computer data from the host computer 239 and a control signal L3 from the system controller 237, and outputs data to be recorded to the laser driving circuit 235. The laser driving circuit 235 receives the control signal L3 (from the system controller 237) and the data to be recorded (from the recording signal processing circuit 234) and outputs a driving current to the semiconductor laser 211.
The system controller 237 receives the address data from the error detection circuit 232 and controls the inputting/outputting of control data to/from the host computer 239. The system controller 237 also outputs the control signals L1 and L3 for controlling the polarity inversion circuit 220, the recording signal processing circuit 234, and the laser driving circuit 235.
The host computer 239, located external to the optical disk drive, controls the inputting/outputting information signals representing e.g., digital video/audio data from the host computer 239 as well as control data.
Hereinafter, the operations of the conventional optical information recording/reproducing device 400 having the above structure will be described.
First, the operation of reading information on the optical disk 200 will be described.
The laser driving circuit 235 is placed in a reproduction mode by the control signal L3 from the system controller 237, and supplies a driving current to the semiconductor laser 211 so that the semiconductor laser 211 is driven to emit light at a predetermined intensity for reading data.
Next, the position of the beam spot 210 along the focusing direction is controlled. It is assumed herein that a common focusing control method such as the astigmatic method is employed, and the description thereof is omitted.
A laser beam emitted from the semiconductor laser 211 is collimated by the collimation lens 212, led through the beam splitter (half mirror) 213, and converged onto the optical disk 200 by the objective lens 214. A light beam reflected from the surface of the optical disk 200, which is diffracted (and hence resulting in a certain distribution of reflected light) in accordance with the information carried on the information track 201, is led through the objective lens 214 to be incident on the optical detector 215 via the beam splitter 213.
The light receiving portions 215a and 215b of the optical detector 215 convert the variation in the intensity distribution of the incident light beam into electric signals (i.e., electric currents), and output the electric signals to the differential amplifier 218 and the additive amplifier 223. The differential amplifier 218 converts the input currents from the light receiving portions 215a and 215b into voltage signals, and then derives a difference therebetween which is output as a differential signal to the LPF 219.
The LPF 219 extracts the low frequency component from the differential signal, and outputs the low frequency component as the signal S1 to the polarity inversion circuit 220. In accordance with a control signal L1 input from the system controller 237, the polarity inversion circuit 220 may allow the signal S1 to pass or invert the polarities (i.e., plus or minus) thereof. As a result, the signal S2 is output to the tracking control circuit 221. The signal S2 is a so-called "radial push-pull signal" which corresponds to the tracking error amount between an actual position of the beam spot 210 converged on the information surface of the optical disk 200 and the target information track 201 that the beam spot 210 should trace.
It is assumed herein that the signal S1 is allowed to pass (without being inverted) in the case where the target information track is a groove track and that the signal S1 is inverted in the case where the target track is a land track. A "target" information track is defined as an information track which carries information to be reproduced or to which information is to be recorded.
The tracking control circuit 221 outputs a tracking control signal to the driving circuit 222 based on a level of the input signal S2. The driving circuit 222 supplies a driving current to the actuator 216 in accordance with the tracking control signal, whereby the position of the objective lens 214 along the direction across the information track 201 is controlled. As a result, the beam spot 210 properly scans on the information track 201.
Once the beam spot 210 is accurately positioned on the information track 201 of the optical disk 200, the currents output from the light receiving portions 215a and 215b, which correspond to the amount of reflected light from the recording marks 207 or the address pits 206, are added by the additive amplifier 223 to be output as an addition signal to the waveform equalization circuit 224. It should be noted that the amount of reflected light decreases when the light spot 210 is on the recording marks 207 and the address pits 206 due to optical interference, causing the outputs of the light receiving portions 215a and 215b to decrease accordingly, whereas the amount of reflected light increases when the light spot 210 is not on the recording marks 207 or the address pits 206, causing the outputs of the light receiving portions 215a and 215b to increase accordingly.
The waveform equalization circuit 224 modulates the addition signal so as to emphasize its high frequency component, thereby reducing inter-symbol interference. The data slice circuit 225 converts the modulated addition signal into a signal sequence of "0" and "1" (i.e., a digitized signal) by digitizing the modulated addition signal at a predetermined slice level. The PLL 226 extracts the data and the reproduction clock from the digitized signal, the data being output as a digital reproduced signal to the input terminals of the AM detection circuit 227 and the selector 228.
If the AM detection circuit 227 detects an AM signal identifying a header region within the digitized signal output from the PLL 226, the AM detection circuit 227 switches the selector 228 so that the digital reproduced signal is input to the address demodulation circuit 231. The address demodulation circuit 231 demodulates the digital reproduced signal so that the digital reproduced signal is converted into a demodulated address which can be suitably processed outside the optical information recording/reproducing device. The error detection circuit 232 determines whether or not the demodulated address that has been read includes an error, and in the absence of such an error outputs the demodulated address as address data to the system controller 237.
As the beam spot 210 reaches a data region in a certain time after the AM detection circuit 227 detected an AM signal, the AM detection circuit 227 switches the selector 228 so that the digital reproduced signal is input to the data demodulation circuit 229. The data demodulation circuit 229 demodulates the digital reproduced signal so that the digital reproduced signal is converted into demodulated data which can be suitably processed outside the optical information recording/reproducing device, which is output to the error correction circuit 230. The error correction circuit 230 corrects any error included in the demodulated data and outputs the demodulated data as the decoded data to the host computer 239.
In the operation of recording information on the optical disk 200, on the other hand, the system controller 237 outputs the control signal L3, thereby indicating a recording mods to the recording signal processing circuit 234 and the laser driving circuit 235. The host computer 239 outputs the information to be recorded (e.g., digitalized video/audio data and computer data) as recording data to the recording signal processing circuit 234. The recording signal processing circuit 234 adds an error correction code to the received recording data, and modulates the recording data for reproduction synchronization, whereby the modulated recording data is output to the laser driving circuit 235.
While the optical information recording/reproducing device is placed in the recording mode by the control signal L3, the laser driving circuit 235 modulates the driving current that is applied to the semiconductor laser 211 in accordance with the received recording date. As a result, the intensity of the beam spot 210 radiated on the optical disk 200 varies in accordance with the recording data, so that recording marks are formed on the optical disk 200 which are in accordance with the recording data.
During the above-described operations, the spindle motor 236 rotates the optical disk 200 at a constant angular or linear velocity.
However, in the above-described conventional optical information recording/reproducing device 400, the identification data in the header region 203, i.e., the output signal (AM signal) obtained from the address pits (pre-pits) formed on the boundaries between a land track and a groove track, is detected based on an addition signal representing a sum of the outputs of the optical detector 215. This implies that the detection accuracy of the identification signal may deteriorate once the beam spot 210 is off-center of the target track. For example, if the beam spot 210 is off-center of the target track, and away from the address pits 206, a corresponding decrease may result in the reproduced amplitude of the addition signal obtained from the header region 203.
Moreover, the beam spot 210 is susceptible to some optical modulation by the pre-pits 206 and the recording marks 207 while the beam spot 210 is in the header region 203 and the data region 204, respectively. As a result, the addition signal output from the additive amplifier 223 receives a degree of modulation, and a correspondingly modulated digital reproduced signal is input to the AM detection circuit 227. This implies that the AM detection circuit 227 may incorrectly determine that the digital reproduced signal derived from the data region 204 includes an AM signal.